This application is based on and claims priority to Japanese Patent Application No. 11-217777, filed Jul. 30, 1999.
1. Field of the Invention
The present invention relates to an engine for a marine vehicle. More specifically, the present invention relates to an improved feedback control system for the engine of a marine vehicle.
2. Description of Related Art
In all fields of engine design, there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued high or higher power output. In pursuit of better fuel economy and emission control, various types of control systems have been developed in conjunction with internal combustion engines. One of the more effective types of controls is so-called xe2x80x9cfeedbackxe2x80x9d control. With this type of control, a basic air/fuel ratio is set for the engine. Adjustments are then made from the basic setting based on the output of a sensor that senses the air/fuel ratio in the combustion chamber in order to bring the air/fuel ratio into the desired range.
Normally, the type of sensor employed for such feedback control is an oxygen (O2) sensor which outputs an electrical signal indicative of the oxygen present in exhaust gases resulting from combustion within the combustion chambers of the engine. Generally, when the output signal voltage is high, little oxygen is present in the exhaust gasses, indicating that a combusted air/fuel charge was rich in fuel. On the other hand, when the output signal voltage is low, substantial amounts of oxygen are present in the exhaust, thus indicating that a combusted charge was rich in air.
A conventional oxygen sensor is normally associated with a wave forming circuit which manipulates the output of the sensor to indicate an xe2x80x9conxe2x80x9d signal when the voltage of the output signal exceeds a reference voltage (i.e., a signal which results when the supplied charge is rich in fuel). On the other hand, the circuit manipulates the signal to indicate that the sensor is xe2x80x9coffxe2x80x9d when the voltage of the output signal does not exceed the reference voltage (i.e., a signal which results from a supplied air/fuel charge which is rich in air).
The control operates on a feedback control principle, continuously making corrections to accommodate deviations from the desired or xe2x80x9ctargetxe2x80x9d air/fuel ratio. Adjustments are made in stepped intervals until the sensor output goes to the opposite sense from its previous signal. For example, if the mixture is too rich in fuel (i.e., the sensor signal is xe2x80x9conxe2x80x9d), then lean adjustments are made until the mixture strength is sensed to be lean (i.e., the sensor signal turns xe2x80x9coffxe2x80x9d). Adjustments are then made back into the rich direction in order to approximately maintain the desired ratio.
Most commonly, the oxygen sensor is the type which utilizes inner and outer platinum coated electrodes. Other commonly used oxygen sensors include Yttria (Y2O3), stabilized Zirconia (ZrO2) or Titania (TiO2) electrode sensors. Additionally, Universal Exhaust Gas Oxygen sensors (UEGO sensors) have recently been developed and are based on a heated conventional Zirconia sensor. The UEGO sensors are able to measure a wide range of air/fuel ratios including a very rich mixture (i.e., 10:1) to a very lean mixture (i.e., 35:1).
Such conventional oxygen sensors include an inner electrode exposed to combustion gases of the engine and an outer electrode exposed to atmospheric air. The oxygen sensor uses ambient air as a basis for determining whether oxygen is present in the exhaust gases, as is known in the art.
One aspect of the present invention includes the realization that known engine sensor assemblies, such as oxygen sensor assemblies, have proven to be inadequate. In particular, it has been found that known combustion condition sensors can have a relatively short useful life span due to the typical operating environments of marine vehicles. For example, as is well known in the art, marine engines typically discharge exhaust gases to the body of water in which the marine vehicle is operating, at a point below the surface of the water, thereby mixing exhaust gases with water upon discharge. Additionally, many 2-stroke engines for marine vehicles are configured to inject water into exhaust gases flowing through the exhaust system immediately downstream of an expansion chamber, to thereby cool the exhaust gases and provide beneficial effects with respect to the tuning of the exhaust system. However, because such exhaust systems can allow saltwater to flow within the exhaust system and possibly to the extreme upstream end of the exhaust system, such saltwater can reach the inner electrode of an oxygen sensor disposed in the exhaust system. The interaction of saltwater with the various exotic and other dissimilar metals used to construct the exhaust system and the oxygen sensor, causes corrosion and ultimately destroys the oxygen sensor.
Other known oxygen sensor assemblies expose the inner electrode of the oxygen sensor to a conduit leading directly to a combustion chamber within the engine. Although this design better protects the oxygen sensor from water that may be present in the exhaust system, other problems are raised. For example, where the oxygen sensor is directly exposed to the combustion chamber, unburnt hydrocarbons may be pushed into contact with the inner electrode, thereby affecting the performance of the sensor. Additionally, the outer electrode is still exposed to ambient air. As such, other problems are raised in allowing ambient air to contact the outer electrode while preventing water from reaching the outer electrode. Thus, it is desirable to provide a control system for an engine of a marine vehicle which reduces the cost of maintenance and manufacturing and extends the operational life of the engine.
Another aspect of the invention includes the realization that although numerous components of an engine for a marine vehicle may be mass produced with a high level of precision, differences result in the operational characteristics of such components despite efforts to maintain consistency of mass produced items. For example, but without limitation, fuel injectors typically include a solenoid which drives a spring biased valve which is biased to a closed position. The springs are mass produced. However, although the springs may appear to be identical, variations have been found between identically sized springs, which results in a difference in the corresponding spring constant. These differences cause the fuel injectors to behave differently from one another, i.e., the speed at which the valve closes according to its bias. Additionally, it has been found that the injection port diameters of one engine body may be different from the injection port diameters of another engine body which are mass produced on the same manufacturing line. These differences, among others, can affect the performance of the fuel injector, and thus the air/fuel ratio delivered to combustion chamber.
Thus, according to another aspect of the invention, an engine for a marine vehicle includes an engine body defining at least one combustion chamber and the fuel injection system. The fuel injection system is configured to form fuel charges for combustion in the combustion chamber. The engine also includes a controller for controlling fuel injection parameters. The controller includes a memory having a predetermined map which includes fuel injection parameters. The controller includes compensation values derived from a test of the engine during operation and defines a fuel injection compensation value as a function of at least one engine operation characteristic. The fuel injection compensation value is determined by operating the engine, detecting a combustion condition of the engine over a range of engine speeds, and determining the fuel injection compensation value which corresponds to a predetermined air/fuel ratio.
By including a compensation value which is derived from a test of the engine itself, the present engine is more accurately controlled because the controller can compensate for the various differences existing in mass produced components, such as springs and injection port diameters.
According to another aspect of the invention, a method for adjusting an engine controller of a marine vehicle engine comprises installing a combustion condition sensor on an engine so as to expose a portion of the sensor to combustion gases within the engine. The engine is then operated using the combustion condition sensor in a feedback control scenario during which a fuel injection compensation value is determined which corresponds to a pre-determined air/fuel ratio. The combustion condition sensor can then be removed and the engine can then be operated without the sensor. Preferably, the combustion condition sensor is an oxygen sensor.
By adjusting an engine controller in accordance with the present method, the controller can compensate for the varying differences present in mass produced components and the cost of the engine can thereby be reduced because the engine does not need to have a combustion condition sensor, such as an oxygen sensor, for example. Furthermore, since the engine controller does not rely oil a combustion condition sensor for operation, the life span of the engine is extended since combustion condition sensors, such as oxygen sensors, typically suffers greatly from corrosion caused by water in the ambient environment in which a marine vehicle is operating, as well as water present in the exhaust system thereof.
Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments which follow.